1. Technical Field
The present invention relates to a work machine having a boom that can be derricked, such as a mobile crane and an aerial work platform.
2. Related Art
Conventionally, a work machine having a boom that can be derricked has been known, which includes a first derricking angle detector that detects the derricking angle of a boom at the base end and a second derricking angle detector that detects the derricking angle of the boom at the front end, and calculates the flexible volume of the boom based on the detected angle by the first derricking angle detector and the detected angle by the second derricking angle detector (for example, see Patent Literature 1).
This work machine acquires the correct working radius by calculating the flexible volume of the boom, and controls the operation of the boom which is working, based on the load factor obtained by the rated load for the acquired working radius and the load acting on the front end of the boom.    Patent literature 1: Japanese Patent Application Laid-Open No. 2001-240392
Here, with the above-described work machine, when the second derricking angle detector fails due to the breaking of the electric circuit of the second derricking angle detector, which is constituted by a potentiometer and so forth, it is not possible to acquire the flexible volume of the boom, and therefore the operation of the boom is halted in order to ensure safety. In this case of the work machine, even if the first derricking angle detector normally works, the boom cannot be operated until the failure of the second derricking angle detector is resolved, and therefore the working efficiency of the work machine deteriorates significantly.